Cheap & Simple Dado Jig

If you follow my woodworking habits, you are well aware that I enjoy using my routers with pattern bits chucked in the collet. The piece I’m working on for the August issue requires repetitive stop cuts that are a 1/4″ wide. As far as I know, pattern bits with a 1/4″ or 1/2″ shank in 1/4″ diameters don’t exist.

If I had a pattern bit, I could clamp a straightedge at my layout line then proceed to routing the dado in just the right location. Another option is to clamp a fence at the appropriate offset to the layout line so I could run the base of the router against the fence and cut the dado where needed. Who wants to constantly measure and mark that offset?

There is a third option. I realize this jig might be old hat if you’re deep into woodworking, but if it’s a new idea, you should give it a try. I use these all the time, they are simple to make (as demonstrated below) and they are so cheap you can make a separate jig for each different bit you use.

The pieces are all cut to size and square at the outset. The 1/4″ plywood is a 1/2″ or so wider than the width of your 3/4″-thick fence piece plus the distance from the edge of the router base plate to the center of the collet. I’ve made these up to 15″ in length, but generally I build them to match the groove length. If you get way long, you’ll need to clamp the far side as well, but that’s getting too far ahead.

First, attach the ¾” fence piece to the ¼” plywood allowing just a fuzz of the fence to stick out past the plywood. Hint: If you’re using a brad nailer with 1” brads, angle the gun as you drive the nail. You don’t want any brad ends sticking through the fence.

Next, chuck your bit into the router then trim the plywood to width as you run the base of the router against the fence. Cut the plywood back to the fence end. This results in the exact cut line of this particular router and bit combination – that’s why it’s important to make a jig with each new setup.

Finish the jig by attaching the 1/2"-thick x 3/4"-wide T-square piece to the jig. This piece has to be squared to the fence (that’s why you leave a small amount of the fence beyond the plywood). A few brads driven through the T-square piece and into the fence holds fine.

To use the jig, align the edge to your layout line, add a clamp (one clamp does the trick if you’re jig is shorter) then run the router base along the fence. If you choose to back up during the cut – something I would not recommend – it’s easy to allow the base to pull from the jig fence. To avoid this mishap, run fully to your stopping point then turn off the router and allow it to come to a complete stop before lifting the tool. (Draw a line along the edge of your router base when you get to the stopping point of your first cut, so you can easily hit the same mark with each pass.)

I used to work in a cabinet shop under [what I consider to be] a master cabinetmaker. He used the method of marking the offset. But after seeing this tip published somewhere, I showed it to him and he was delighted to see that it made our dados more accurate and considerably increased our efficiency. I made many sizes of them, up to 4 feet long for the router and some up to 12 feet long for the circular saw. I should note that our method was to rabbet joint all carcass parts and dado all shelves as well as dadoing all faceframes to fit the carcass so each cabinet had lots of dado work.

Here’s a few extra tips:

1.) One feature I added to my jigs were to make them work two sided by placing the fence in the middle of the jig – one side was for a 3/4″ bit, the other was for 1/2″. Of course we used a lot of plywood so we had ‘true’ 3/4″ jigs as well as undersized 3/4″ jigs. It pays off to know the difference and to gauge your plywood before dadoing.

2.) Mark one edge of the router base and only use that edge to cut the jig and perform the dadoing. While most router bases are centered pretty well, I have found some that were off by up to 1/16″ which means your jig will be off by the same amount causing your dado to be offset by the same amount. Even if you’re sure you think your router is perfectly centered, there’s no harm in being cautious.

3.) I prefer using 3/4″ plywood for the fence and T-square. I just trust it’s stability and straightness. Seven ply will work but 13 ply is better.

4.) You should really nail AND glue the fence to the jig base lest the fence will begin to wiggle after some use.

5.) Try not to skimp on the 1/4″ plywood by using hardboard or luan. Use 5 ply european birch plywood. Luan tends to give a chippy/unreliable edge and the darkness of hardboard makes seeing the cut mark difficult.

6.) Setting the jig up for use with a plunge router base makes creating stopped dados much easier.